The present invention relates to a tire vulcanizing press and more particularly to a hydraulic tire vulcanizing press of the type which includes a hydraulic cylinder for tightly closing a die assembly with a raising and lowering table disposed between the hydraulic cylinder and the die assembly.
A hitherto known tire vulcanizing press of the above-described type is generally constructed such that the rasing and lowering table has a working stroke of about 1,000 mm in the case of tires for a passenger car and about 2,000 mm in the case of tires for a truck, bus or the like in order to ensure that a green tire to be vulcanized is placed on a lower die half of the die assembly without interference with any part of the press. It is natural that the hydraulic cylinder for tightly closing the die assembly is designed to have a long working stroke corresponding to the working stroke of the raising and lowering table. Since the conventional tire vulcanizing press is constructed in the above-described manner, there is a fear that the die clearance between both the upper and lower die halves exceeds an allowable limit when a reduction in hydraulic pressure takes place in the press cylinder due to leakage from packing in the hydraulic piping or the like and thereby the thermal energy carrier for vulcanization (steam, hot water at a high pressure, high temperature and high pressure gas or the like) maintained in the die assembly, leaks therefrom. To prevent an occurance of the leakage of thermal energy carrier there has already been proposed an arrangement of an expensive breach lock ring, control of the hydraulic pressure with the aid of a pressure switch, etc. However, it has been found that these proposals are not always satisfactory as means for preventing an excessive die clearance between both the upper and lower die halves.
Thus, the present invention is intended to obviate the drawbacks inherent to the conventional tire vulcanizing press as described above. A tire vulcanizing press in accordance with the present invention is constructed such that a die assembly is tightly closed by means of a press cylinder with a raising and lowering table (lift table) disposed therebetween, wherein a spacer is displaceably disposed between the press cylinder and the raising and lowering table (lift table) so that a predetermined die closing force is transmitted from the press cylinder to the die assembly via the spacer and the raising and lowering table when the die assembly is to be tightly closed.
Hence, it is an object of the present invention to provide a tire vulcanizing press which is able to reliably prevent an occurance of excessive die leaking with the aid of mechanical means.
It is another object of the present invention to provide a tire vulcanizing press which is safe to operate.
It is a further object of the present invention to provide a tire vulcanizing press which is simple in structure and thus can be manufactured inexpensively.
Due to the arrangement that a spacer is displaceably disposed between the press cylinder and the raising and lowering table (lift table) and a predetermined die closing force is transmitted from the press cylinder to the die assembly via the spacer and the raising and lowering table, when the die assembly is to be tightly closed, is ensured that the spacer is caused to move to a position located at the central part of the raising and lowering table in correct alignment with a press rod of the hydraulic cylinder after the raising and lowering table is lowered, the press cylinder is designed to have a very short working stroke which is dimensioned sufficiently to exert a predetermined die closing force on the die assembly. The working stroke is less than the allowable die opening limit, and any excessive die opening is reliably prevented by the minimized working stroke of the press cylinder and the arrangement of the spacer when a reduction in the hydraulic pressure takes place in the press cylinder due to mechanical failure or the like. As a result, no danger of leakage of the thermal energy carrier for vulcanization is created. Furthermore, due to the arrangement that the press cylinder is designed to have a very short working stroke with the spacer disposed between the press cylinder and the raising and lowering table, it is ensured that the die assembly is closed tightly closed quickly and correctly.